1. Field of the Invention:
This invention relates to a brake device including an actuator elastically contractible in its axial direction upon applying internal pressure for actuating the brake device. More particularly this invention relates to a brake device suitable for use in arms for robots or manipulators.
2. Description of the Prior Art:
Brake devices for use in robot arms have been known. For example, a brake device including a pneumatic piston and cylinder assembly has been used. With such a brake device, a lever is pivotally supported at its mid portion and has one end loaded by a spring and the other end connected to the pneumatic piston and cylinder assembly. When the piston and cylinder assembly is extended or retracted, a brake shoe secured to the lever is urged against a brake drum connected to a pulley or rotating body, thereby restraining or braking its rotating movement. In order to urge the brake shoe to the brake drum against the spring force of the spring acting on the one end of the lever to produce required braking force, the piston and cylinder assembly must exert a great force on the other end of the lever provided with the brake shoe. For this purpose, the piston and cylinder assembly is needed to have a large diameter cylinder bore which makes the piston and cylinder assembly, itself bulky and heavy.
A brake device using such a bulky and heavy piston and cylinder assembly is expensive to manufacture and difficult to handle and consumes a great amount of pressurized fluid. It has been expected for many years to provide a brake device particularly for use in a robot arm, which is light and small-sized and easy to treat and consumes a small amount of compressed air.
There have been various kinds of actuators for robot arms. Pneumatic actuators among them have been accepted because they are susceptible to overload and high in safety for humans bodies and do not suffer from heating due to their deformation. However, most of pneumatic actuators hitherto used are pneumatic piston and cylinder assemblies usually made of iron which are excessively heavy in comparison with their operating forces.
On the other hand, actuators of air bag type have been also known. In this case, contractive forces resulting from expanded diameters upon applying control pressures into the actuators are used as operating forces for robot arms. Such actuators are of light weight and do not include sliding parts and therefore do not suffer from difficulties due to friction and air leakage.
For example, a wire extends about a pulley rotatably supported by one end of a frame, and both ends of the wire are connected to one end of the above mentioned actuators, respectively, whose other ends are pivotally connected to a suitable stationary member. With this arrangement, internal pressure is supplied into one pneumatic actuator and exhausted from the other actuator to rotate the pulley.
However, such a pneumatic actuator encounters a difficulty in control due to fine vibration or oscillation resulting from the inherent elasticity of the actuator itself. For example, when the pulley or a member fixed to the actuators is held in place after the pulley or the member has been rotated by a desired angular displacement, the actuators often go into fine oscillation. Moreover, if the pressurized fluid is inadvertently exhausted from the pneumatic actuators, the driving device for the robot arm is not longer restrained, so that it will be moved unintentionally to cause further trouble.